Read Sheet1!A:A then mark corresponding cells in Sheet2

I'm after a formula/VB script to perform a fairly simple task (hopefully).

I need it to,
1 - read Sheet1!A:A
2 - then mark (with a 1) on sheet2 in the corresponding cell

e.g the data in cell Sheet1!A1 would mark Sheet1!B2

There will be another 100 more branches to be input to Sheet1!A:A

Hope this makes sense.
Many thanks

Ashley